Conventionally, in video game machines or computers, an icon or a position on the display screen is pointed by moving a cursor on the screen with direction keys, a mouse or the like (hereinafter, referred to as “conventional cursor moving means”). The cursor is moved as follows: The direction and the amount of movement of the cursor are input through the conventional cursor moving means and detected every predetermined period. The cursor display position is moved to a location which is obtained by adding the amount of movement regarding the direction of the movement to the current cursor display position.
FIG. 14 illustrates a method of moving the cursor with a mouse. By movement of a mouse from a position 802 to a position 802′, a cursor 801 moves. If it is supposed that the amount (ΔX, ΔY) of the movement of the cursor is input through the mouse 802, the display position (X, Y) of the cursor 801 moves to a display position (X+ΔX, Y+ΔY).
Another cursor moving method developed recently uses a pointing device to point a position on the display screen directly. The pointing device captures the image of the display screen with an imaging sensor, such as a CCD camera, mounted to the tip thereof, and outputs information about where in the image captured by the imaging sensor the certain light from the light emitting body mounted above or around the display screen is positioned. In this cursor moving method, the cursor is moved as follows: The intersection of the optical axis extending from the central point of the imaging sensor to the display screen in the direction of the normal line and the display screen is calculated from the information output from the pointing device. The cursor is displayed at the position of the intersection. In this way, the cursor is moved to follow changes of the direction pointed by the pointing device.
FIG. 15 illustrates the method of moving the cursor by using the pointing device. By change of the direction from that pointed by the pointing device 803 to that pointed by the pointing device 803′, the cursor 801 on a display screen 800 moves from a display position (X, Y) to a display position (X′, Y′).
A method of calculating the cursor display position (the intersection of the optical axis of the imaging sensor and the display screen) with a pointing device is disclosed in JP-A-8-226793, for example. In this method, infrared spots are displayed at the left and right edges of the display screen. A CCD camera provided at a tip of an imitated gun captures an image. The position shot by the imitated gun on the display screen is detected based on the position of the infrared spots in the captured image.    Patent Document 1: JP-A-8-226793